Delivery of unique skin treatment products always presents a problem to the formulator. Many of the most useful skin-therapeutic agents are biologically active, and are therefore not useful if there activity is compromised in any way. This means the formulator must choose a delivery vehicle that will be compatible with the active, not causing a degradation of the compound's activity. Maintaining the stability of the active components of a formulation may however sometimes be at odds with the design of a cosmetically acceptable vehicle. Although the modern consumer is more demanding with respect to getting a therapeutic effect with her cosmetics, she ordinarily will not at the same time sacrifice the aesthetics of the product to obtain this. Thus, the formulator is frequently presented with the dilemma of how to provide the maximum therapeutic effect in a vehicle that is cosmetically elegant, yet not necessarily innately compatible with the desired active agent.
This problem is seen particularly in the preparation of gel-type compositions. A gel vehicle is particularly popular now, for a number of reasons: in its most desirable incarnation, a gel, specifically a water-based gel, is cooling, gentle, and non-greasy on the skin. However, achieving maximum efficacy of incorporated actives while fully retaining aesthetics of the vehicle presents substantial difficulty in gel formulation. Incorporation of other useful cosmetic ingredients can cause a loss of clarity, rendering the gel cloudy and less attractive. Similarly, many types of actives can cause a disruption of the gel structure, which can cause instability of the product as a whole, and/or result in a product that has an unacceptable feel when applied to the skin. This problem is particularly difficult when the active components comprise one or more acids, which are frequently present in the composition as electrolytes, as electrolytes can seriously interfere with the maintenance of a stable, clear gel product. A particularly desirable gel vehicle is one in which a biliquid foam is dispersed, such as is described in WO 97/32559. A biliquid foam is advantageous because it permits the incorporation of a relatively large quantity of oil, and oil soluble actives, into an aqueous phase with the use of a very small amount of surfactant. However, the gelling of the aqueous vehicle containing the biliquid foam is quite difficult in the presence of electrolytes, particularly when the pH is acidic.
There thus continues to be a need for improved aqueous gel formulations that can be used to deliver the necessary therapeutic agents while at the same time retain stability and the elegant texture consumers expect from a gel product. The present invention provides such a product.